Bound by Flesh is a sad, unsettling, absorbing documentary about Daisy and Violet Hilton, conjoined twins born in the early 1900s whose repulsed mother sold them as infants to a money-grubber who immediately put them on display and forced them into a show business career as sideshow “freaks.”

Cash cows passed from one lowlife huckster to another, the attractive sisters became musical prodigies and hugely popular, internationally famous vaudeville attractions, performing alongside and rubbing shoulders with top-of-the-bill attractions like Bob Hope, Harry Houdini and Fanny Brice. Privately, the siblings were constantly physically and psychologically abused by their sleazy Svengali of a manager Myer Meyers, who kept them hidden and isolated from the world and bilked them of most of their enormous earnings. In 1931 at age 22, the sisters finally won help from advocates who hauled Meyers into court. In a case publicized worldwide, Violet and Daisy gained their emancipation. But, once rid of Meyers, the sisters were not only entirely dependent upon each other but also unprepared for most aspects of day-to-day reality, romantic relationships and navigating the often-cruel vagaries of show business. Their inevitable downward spiral has already been the subject of several books and Bill Russell and Henry Krieger’s cult Broadway musical Side Show.

Leslie Zemeckis (author of Behind the Burly Q: The Story of Burlesque in America) directs the film with a fresh eye, bringing to it equal parts sympathy, excellent historical insight and fascination for the long-gone world of traveling carnivals and circuses. The overly long movie unfolds through compelling contemporary interviews, voicing by Nancy Allen and Lea Thompson, clips from the sisters’ appearances in the 1932 film Freaks and the tawdry 1952 screen “autobiography” Chained for Life, as well as scant archival footage, the latter of which gets reprised too many times. But the story of two ultimate outsiders is so compelling and heartbreaking that the movie triumphs.